


Fantasy

by theonetruenorth



Series: Shadowhunters headcanons [20]
Category: Shadowhunters (TV), The Mortal Instruments Series - Cassandra Clare
Genre: Anal Fingering, Anal Sex, Bottom Magnus, Embedded Images, Fantasy Fulfillment, M/M, Office Sex, Oral Sex, PWP, Safer Sex, Top Alec
Language: English
Status: Completed
Published: 2017-02-25
Updated: 2017-02-25
Packaged: 2018-09-26 18:26:07
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,478
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/9915344
Author URL: https://archiveofourown.org/users/theonetruenorth/pseuds/theonetruenorth
Summary: “Mhmm,” Magnus hummed as they broke apart and he rocked his hips minutely, the slight movement enough to make them both shiver. “This is getting dangerously close to one of my fantasies, so maybe we should stop, if you don’t want this to go any further.”“What fantasy?” Alec murmured, craning his neck up again to brush his lips against Magnus’ but the warlock teasingly moved just out of reach.“Well,” Magnus started, looking at Alec through half-closed eyes and with a hint of a smirk tugging at the corner of his mouth, “I have never had sex inside the Institute.”





	

**Author's Note:**

  * Translation into Русский available: [Фантазия](https://archiveofourown.org/works/12031368) by [fandom_Shadowhunters_2017](https://archiveofourown.org/users/fandom_Shadowhunters_2017/pseuds/fandom_Shadowhunters_2017), [Teapot with treasures (Questie)](https://archiveofourown.org/users/Questie/pseuds/Teapot%20with%20treasures)



“Is your head hurting again?”

Alec opened one eye at the sound of his boyfriend’s voice, but otherwise he didn’t budge. If he avoided moving too much, he could pretend his head wasn’t trying to split in half.

“I have a feeling there is no good answer here,” he eventually replied. Magnus was going to be angry that he tried working while suffering from a headache, but he was going to be even more mad if Alec tried to hide it from him.

“That’s probably because there isn’t.” Magnus shook his head and left his spot in the doorway, closing the door behind him with a soft click. “Darling, I thought you said you aren’t going to be very busy today?”

“It’s just Clave being a nuisance out of nowhere.” Alec waved at the stack of papers on the desk and the laptop with open files. He still tried not to move from his current position, leaning back with his head resting against the cushy surface of the chair. “It’s the new treaty with the Seelies.”

Magnus came to stand next to him and leaned on the desk with one hip, peering at the documents with what seemed like boredom.

“If it’s legal matters then I can help you with it, if you wish.”

“Nah, I’m almost done anyways,” Alec sighed. “It’s just… you know how it is with the Seelies. Every word of the contract must be precise to avoid misunderstandings.”

“And so that they can’t twist it around and find a loophole,” Magnus said, nodding in understanding. “Unfortunately, I’m familiar with their tactics.”

“I already wrote it, I just need to double-check it before I send it back to the Clave so that they can approve it. Only then I can present it to the Seelie Queen.” Alec reached to brush his knuckles affectionately over the back of Magnus’ hand. “It’s just stupid bureaucracy.”

“Writing a contract with the Seelies would give anyone a migraine.” Magnus smiled at the small gesture and entwined their fingers together for a moment. “I might be able to help with that too. Here, let me.”

Without really waiting for Alec to reply, Magnus moved so that he could sit in Alec’s lap. Alec merely raised an eyebrow at him, even as his hands automatically shifted to grab at Magnus’ hips.

“Comfortable?”

“Quite.” Magnus smirked. “You’re lucky your chair is so big. Now, be still and let me work my magic.”

Alec snorted in amusement but regretted it immediately when his head responded with a sharp stab of pain. Magnus made a quiet, disapproving sound, before placing his fingers over Alec’s temples. He rubbed his thumbs in small circles and with each gentle pass the pain lessened a little bit. Alec closed his eyes in relief and his headache slowly ebbed down, chased away with soothing pulses of magic he could feel against his skin.

It took only a minute or two before the pain was gone and Alec hummed contently, placing his hands on the top of Magnus’ thighs and squeezing lightly. His eyes were still closed.

“Better?” Magnus asked, brushing his thumb tenderly over the arch of Alec’s brow, smoothing it out.

“Much,” Alec whispered. “Thank you.”

“You’re welcome, darling.”

Alec opened his eyes and looked at Magnus, who seemed quite content to remain seated on him, his thighs bracketing Alec’s own hips and their bodies fitting together snugly in the chair. Alec didn’t even have to think about it, he just tilted his head a little and Magnus was leaning in, encouraged by the silent offering.

They kissed for a while and it started out sweet and slow, like it often did. Alec closed his eyes again and just let himself enjoy the way Magnus’ tongue stroked his and the warm breath washing over his cheek with every exhale. He rubbed his hands over Magnus’ strong thighs and up, until he could grab two handfuls of Magnus’ ass and knead gently.

“Mhmm,” Magnus hummed as they broke apart and he rocked his hips minutely, the slight movement enough to make them both shiver. “This is getting dangerously close to one of my fantasies, so maybe we should stop, if you don’t want this to go any further.”

“What fantasy?” Alec murmured, craning his neck up again to brush his lips against Magnus’ but the warlock teasingly moved just out of reach.

“Well,” Magnus started, looking at Alec through half-closed eyes and with a hint of a smirk tugging at the corner of his mouth, “I have never had sex inside the Institute.”

Alec moved his head away and blinked owlishly at him.

“And I've definitely never been fucked on the desk in the office of the head of said Institute.”

Alec was pretty sure the look of surprise on his face made him look like a fool, since Magnus laughed and patted Alec’s cheek fondly.

“Oh my, I believe I broke you,” Magnus said, amusement still clear in his voice. “I think that’s enough teasing. How about you finish your work and we go home, hmm?”

Magnus moved to slide off from Alec’s lap but a pair of strong hands still holding onto his ass refused to let him go.

“Magnus…”

“Don’t worry about it, darling, it was just a silly thought,” Magnus said hesitantly, as if he was not quite sure how to interpret the peculiar look on Alec’s face.

“I--”

“I didn’t mean to make you uncomfortable...”

“Lock the door,” Alec said, giving Magnus’ cheeks a firm squeeze. His voice was low and raspy and it made Magnus shiver in reaction; he listened and snapped his fingers sharply. There was a faint sound of lock turning in the door and a familiar hum of magic as a privacy ward settled over the room, added by Magnus. Just in case.

“Alexander, I--” Magnus didn’t get to finish his sentence as he yelped in surprise as Alec pushed out of the chair and stood, his hands still on the warlock’s ass, holding him up. Before Magnus had a chance to gather his wits, Alec deposited him on the edge of the desk and then kissed him once more. It was heated and almost violent and by the time they separated for much needed air, Magnus’ lips looked tender and bruised from the sheer force of it.

Magnus was half-hard already just from kissing alone and so was Alec, judging from the familiar hardness digging into Magnus’ thigh where he lodged it in between Alec’s legs, giving him something to grind against.

“Not that I’m complaining, far from it,” Magnus said a little breathlessly as Alec sat back down in his chair and scooted it closer to the desk, until he was in right between Magnus’ spread legs, “but you know I was just joking, right?”

Alec looked up at him from beneath his lashes.

“About the fantasy?” He asked, reaching up to unbutton Magnus’ shirt, one button at the time.

“No, the fantasy part is real,” Magnus admitted and gasped when Alec rubbed one of his nipples through the silk fabric of his shirt. “I meant the part where you feel like it’s something that you need to do. You don’t have to.”

“I want to,” Alec said lowly, finally popping the last button and revealing his prize. He hummed quietly, clearly pleased with himself. “I want to give you something that no one else has ever given you.”

“Alec--”

“Do _you_ want me to, or not?” Alec asked, pausing for a moment with his hand resting on Magnus’ stomach, just a short distance away from the prominent bulge in his pants. Magnus gazed down at him and for a moment it seemed like he was about to refuse, not wanting to push Alec past his comfort zone. But the expression that Alec was sporting right then must have betrayed his thoughts, because Magnus remained silent as he looked into Alec’s eyes.

Alec was perfectly aware that Magnus had done _many_ things in his long life and sex was not the exception. Every fantasy and kink that Alec could think of? He was pretty sure that Magnus had done it before. He had no way of surprising Magnus in bed and while that usually wasn’t a problem… he really, really wanted to do this. To give Magnus a memory of something that was his first, that was completely unique and new to _both_ of them. But he was hesitating, unsure if his actions were appreciated or not. He had not felt so uncertain in a very long time, not since those first months into their relationship, when sex and intimacy were still a new concept for him.

Magnus, as always, could read him like an open book.

“Yes,” Magnus’ gaze softened a bit and he cupped Alec’s cheek, smiling a little as Alec nuzzled into it, “I want you to.”

With that simple reassurance the doubt seemed to melt away from Alec’s eyes as he craned his head up for another kiss, one that Magnus willingly gave him. Magnus gasped into it when Alec started to palm him through his pants, massaging the rapidly filling cock through layers of fabric. It wasn’t long before Alec was breaking away from the kiss and his long, nimble fingers were undoing Magnus’ belt and pulling his pants down, yanking them off his legs along with his boots. The skin-tight boxer briefs underneath were made of fiery-red silk and they were so _Magnus_ that it almost made Alec chuckle in amusement. Almost.

He was going to enjoy ruining them.

Magnus let out a choked-off, breathless sound when Alec ducked his head and licked a long, wet stripe over the entire length of his cock. The fabric became wet almost instantly, clinging to sensitive skin as Alec repeated the motion again and again. He wrapped his lips over the crown, giving it a light suck.

“Oh, fuck it,” Magnus gasped when Alec let him go for a moment and with a snap of his fingers the boxers were banished right off his body. Magnus wasn’t interested in where they ended up; they could have landed on Maryse’s head, for all he cared. Another flick of his wrist made two foil packets - lube and a condom - appear out of the thin air and land unceremoniously in Alec’s lap.

“Someone’s impatient,” Alec laughed even as Magnus sent him an unimpressed glare. He lightly stroked his fingers up Magnus’ cock from root to tip, making Magnus shiver almost violently. With his other hand he nudged one of Magnus’ legs further up, until he got the hint and placed his feet on the armrests of the chair.

Being on the performing end of a blowjob had never been Alec’s favorite activity, unlike Magnus, who seemed to think it was the best thing in the world. Alec was not a fan of the taste of come, even if he didn’t hate it, and he never really got over feeling somewhat self-conscious. He was sure he looked ridiculous with his mouth filled with cock and his lips wrapped around it, no matter how many times Magnus assured him that he looked _fucking incredible_. There was a small part of him that never really believed it was true.

Alec did, however, _love_ the way Magnus reacted to him.

“Fuck,” Magnus groaned as Alec took him in and he was enveloped in a hot, wet mouth. Magnus reached behind him blindly to shut down the cover of the laptop - Alec made a mental note to thank him later, they couldn’t have all that hard work go to waste, after all - and move it out of the harm’s way before his arms gave out and he leaned back on the desk. One of his trembling hands wove itself in Alec’s hair, cradling his head in a gentle grip. He tugged on his hair, just a bit, and Alec groaned, the additional vibrations making Magnus moan.

Alec closed his eyes and relaxed, leaving Magnus in charge of his movement and allowing him to dictate the pace. The fingers woven in his hair steered him, moved him faster or slower, depending on what Magnus wanted. It was controlling and dominant and Alec felt like he could do it forever. He could let himself be used, so gently and lovingly, and be the instrument of Magnus’ pleasure. He was aware of his own cock straining against the zipper of his jeans, almost painfully so, but the thought of touching himself or relieving the pressure didn’t even cross his mind. He would have to abandon his task and that just wouldn’t do, not when Magnus still had a use for his mouth.

For the next couple of minutes Alec concentrated only on making Magnus lose his mind. The air around them seemed to be filled with electricity and every touch, every smart twist of tongue, every quiet hum spurred Magnus on further. Slick fingers trailed over Magnus’ balls and even further down, until they could massage at his entrance, slipping in effortlessly once the muscles relaxed. Two at first and then eventually three, stroking and prodding and stretching.

The room was echoing with the sounds of sex, with the loud noises that escaped them both. Alec looked up without stopping, his gaze sliding over the quivering muscles of Magnus’ belly and up his toned chest until he met Magnus’ eyes. He felt a little light-headed once he realized that Magnus had dropped his glamour and that his eyes were barely half open but focused only on him, on Alec’s lips wrapped around the hard cock.

With a shaky arm Magnus raised himself back up into a more or less sitting position. Alec tried not to think about the picture they must have made. Magnus with his shirt open and pooling around his elbows, sitting with his ass naked on the edge of the desk, legs splayed shamelessly open and trembling where he supported them on the armrests of the chair. Alec between his thighs, lips wrapped around Magnus’ cock, three knuckles deep inside of the willing body laid out before him. Magnus’ hand tangled in his hair. The absolutely filthy, _delicious_ sounds that filled the room.

The head shadowhunter of New York, sucking off and fingering the High Warlock at his desk, right in the middle of the Institute.

“Oh, Alec,” Magnus moaned as he caressed his free hand over Alec’s cheek and jaw. Alec could feel those fingers pressing against his skin and he knew that Magnus was feeling himself moving in and out of his mouth. Alec never really mastered deepthroating, his gag reflex being sensitive as it was, but it didn’t matter. “That’s enough, love.”

Alec pushed the chair away once more as he stood up, mouth latching onto Magnus’ own, letting the warlock taste himself on his tongue. Both of their hands reached for Alec’s zipper at the same time and Alec undid it with trembling fingers. Magnus was still sucking on Alec’s tongue even as his hand reached into Alec’s pants and pulled his cock out, giving it a couple of firm strokes. Alec didn’t need more encouragement, though; he was already hard and leaking.

Once they came up for air Magnus shimmied down from the desk until he could stand in front of his boyfriend and shrug off the shirt still tangled around his elbows. It left him completely naked, save for the multiple necklaces still dangling around his neck. His hands ripped open the condom package and quickly slipped it on Alec’s cock. With a last, hard kiss, he turned around and braced his hands on the desk.

“Come on,” Magnus purred as he looked over his shoulder and his heated gaze filled Alec with pure _want_ , “fuck me, darling.”

It was as much as request as it was a command and Alec was unable to refuse.

He pushed inside, slowly but steadily, mindful of the sharp inhale that left Magnus’ lips. Alec stroked a soothing hand down Magnus’ back, the skin soft and warm underneath his fingertips. Alec closed his eyes for a moment, letting his lover adjust. It never took long, but Alec used the momentary respite to center himself, to just feel the tight, welcoming heat of Magnus’ body.

The first thrusts started slow and careful, as they always did. Alec kept one hand on the small of Magnus’ back and the other cupped around Magnus’ hip as he built up the tempo.

“Oh god,” Magnus groaned as his arms gave out and he slumped down, his chest pressing against the desk and his forehead resting against the cool wooden surface. His back arched tantalizingly and his hips shifted and Alec could _see_ the exact moment the angle was just right. Magnus’ back went taunt for a second or two before his body relaxed again, all but melting against the desk. Alec tried to get that angle again and was rewarded with a long moan when he found it.

Alec had to close his eyes, knowing that it was going to be his undoing, this sight of Magnus bending over for him, letting him do whatever he wanted. There was something exhilarating and strangely empowering about this, about Magnus being stark naked while Alec was still fully clothed. About the way Magnus was trapped between Alec’s body and the desk, unable to do anything but just lie there and _take it_.

“Fuck,” Alec cursed as both of his hands drifted to Magnus’ hips to grab them tightly, surely leaving fingertip-shaped bruises he would find there later on, “you feel so good. Can you take more?”

“ _Yes_ ,” Magnus mewled as he widened his stance and spread his legs a little more. His palms were splayed on the surface of the desk and he curled them into fists as the head of Alec’s cock grazed against his prostate. “Harder, love. Please, just…”

Magnus’ voice trailed off as he trembled once more and Alec swallowed hard against the lump in his throat. Magnus was beautiful like this, wanton and needy, too focused on his own pleasure to properly form words. This centuries-old warlock, losing his composure because of him.

Alec used his grip on Magnus’ hips to thrust harder, to yank him back just as he was pushing in and it tore new, blissful sounds from Magnus’ throat. He cried out at a particularly rough thrust and his hands scrambled for purchase, for something to hold onto as Alec fucked him senseless. He found nothing and his palms slid across the wood aimlessly.

“Oh!” Magnus keened when Alec’s punishing pace picked up. Alec could feel heat pooling low in his belly, like molten lava that grew hotter with every calculated thrust. “Oh god, Alexander, I’m going to come,” Magnus groaned, each forceful impact of their bodies colliding making his hips bump into the desk; he was going to have bruises later. The necklaces around his neck jingled as they slid against the wooden surface, set in motion with each strong push and pull.

Alec wasn’t going to last much longer. He could feel sweat dripping down his back, his legs trembled as he struggled to keep up the pace. It was impossible for him to last, not when Magnus sounded so very lost in pleasure. Not when Alec could see his cock driving into the willing body, again and again and again. Knowing he was so close, Alec reached around to wrap his hand around Magnus’ cock, neglected until that point. It was hard and hot and leaking and Magnus choked on air as Alec started jerking him off. Alec’s other hand went on Magnus’ back, pushing him down onto the desk, keeping him exactly where Alec wanted him.

It didn’t take long before Magnus was coming with a shout and Alec had a moment of clarity to remind himself to thank Magnus later for the privacy ward before he was coming himself. It almost took him by surprise and he pushed deep into Magnus’ warm body as the waves of bliss overtook him.

He came to his senses after a minute, realizing that his forehead was resting on the hot skin of Magnus’ back and his body was still pinning him to the desk. But Magnus didn’t seem inclined to move, breathing heavily as he came down from the high.

Alec raised himself slightly so that his weight didn’t crush his boyfriend and he brushed his hand through Magnus’ hair, already impossibly disheveled.

“You okay?” Alec asked, stroking his thumb over the shell of Magnus’ ear gently, a small gesture that made Magnus’ lips twitch into a smile.

“Oh, I'm _fantastic_ , but I think you broke me,” Magnus croaked, sighing contently as Alec placed his hand over Magnus’ on the table and tangled their fingers together, “but I guess I asked for this, so I can’t really complain.”

 

**Author's Note:**

> Every fic in this series is first posted to my tumblr and I usually upload it to AO3 with a delay. If you want to read my stories as soon as I finish them, follow me there: theonetruenorth.tumblr.com
> 
> Beta-read by [brizzbee](http://brizzbee.tumblr.com/)


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